In the manufacture of molded records, such as audio records and the more recently developed video records, a plastic composition is molded between a pair of metal plates referred to as stampers which have the information desired to be molded into the record defined in the surface thereof. The stampers are the end product of a multi-step replication process. The initial step in the replication process is to record the information desired to be molded into the record on a magnetic tape. The recorded magnetic tape is then used to control a cutting tool which cuts an information track in a flat, disc-shaped member referred to as a recording substrate. The resulting recording substrate has the surface relief pattern desired to be molded into the final record and could conceivably be played back on suitable apparatus to reproduce the recorded information. However, it is not practical to use the recorded substrate for playback because of, among other things, the extremely high cost involved in cutting the recording into the recording substrate. The recording substrate is, however, used in the replication procedure which ultimately results in the production of the stampers.
The next step in the replication process is to electroform a metal replica on the recorded surface of the recording substrate. The recording substrate is mounted and rotated in the cathode position of an electroforming apparatus while a supply of the metal to be electroformed on the substrate, typically nickel, is provided at the anode of the electroplating apparatus. The electroforming of the replica on the recording substrate is conducted by electroforming methods well known in the art. After a sufficient amount of metal has been electrodeposited on the recording substrate, the resulting electroformed part is then separated from the recording substrate. The resulting electroformed part is referred to in the art as a master, and is a negative replica of the starting recording substrate.
The master is in turn duplicated a number of times until the resulting replicas start to show significant loss of fidelity to the master on which they are electroformed. The electroformed replicas formed on the master are referred to in the art as molds or mothers. The molds or mothers are positive copies of the original recorded substrate.
Each of the molds or mothers is then, in turn, also replicated several times in a similar electroforming process to produce a third series of electroformed metal parts referred to as stampers. The stampers are negative replicas of the original recording substrate. As noted above, it is the stampers which are ultimately used as the molding plates to press molded records. The record molded on the stampers should be an accurate replica of the original recorded substrate, and on playback should result in a high fidelity reproduction of the information initially recorded on the recording substrate.
Many problems are, however, encountered in the electroforming process. One of the major problems encountered is that often the metal is electrodeposited on the part to be duplicated such as the recording substrate, the master or the mold (hereinafter referred to collectively as matrixes), in a non-uniformly thick layer so that the electroformed part has varying thicknesses across its diameter. The non-uniform deposition causes problems in the further replication of the master and molds, and is especially troublesome with regard to the stampers. The nonuniformity in thickness can cause defects in the molded records and also substantially reduce the useful life of the stampers.
A further problem encountered in the electroforming process is that often foreign particles, or even excessively large particles of the metal desired to be plated onto the replicas, are attracted to the surface of the matrix being duplicated. If these particles are not removed from the surface before any substantial amount of plating occurs, the particles can cause surface and internal defects in the resulting replicated part.
What would be highly advantageous would be an apparatus which would improve the uniformity of the plating and also which would prevent or substantially reduce defects caused by the presence of foreign materials or large pieces of metal on the surface of the matrixes during electroforming.